Easier Way for 2 inch Drain? (1 Piece Shower In Basement)

Installing a 1 piece fiberglass shower in the basement.

Began breaking the concrete slab to rough the drain towards the center of the shower for P-TRAP installation.

Is there an easy way to connect http://www.oatey.com/graphics/products/drains/42050.gif

with the P-TRAP?

I mean it's not like the back of a bath tub where I have access or like installing a shower on a main floor / second floor where I can work below the shower.

Do I assume, rough the 2inch pipe, glue the P-trap, screw on http://www.oatey.com/graphics/products/drains/42050.gif onto the base of the shower, take the exact measurement between the P-TRAP and http://www.oatey.com/graphics/products/drains/42050.gif, glue a piece of pipe onto http://www.oatey.com/graphics/products/drains/42050.gif and force the shower into the P-TRAP?

Does anyone know of a better way, I know that some http://www.oatey.com/graphics/products/drains/42050.gif are adjustable, meaning instead of glue to the 2 inch pipe that goes into P-TRAP, it has a rubber gasket, but the concept is still the same, meaning the measurement has to be exact with no room for error?

Thanks
Avellino

Just make good measurements and all will be fine. If you don't think you can do it, hire a plumber. Most of us can do that kind of install with our eyes closed...lol.

Good luck.